oriundi ex EtrusciI want to see an explanation in grammar about this form of gerundive -undus (not -endus).I searched in Gildersleeve but couldn't find it.Is it an older form, like servos for servus ?So, please point me such a place in Gildersleeve or Allen&Greenough.

Hi Sebastos, thank you.Yes, I can see the example audiundum 'st there.(Now I see such a coloquial Latin for the first time.To read such, the knowledge obtained from grammar would be fully used. What Latin I have read are all philosophical or of the periods later than middle ages.To read them there is hardly a chance to use that grammatical knowledge other than the syntax of the noun cases, i.e. the use of gen., dat., and abl..)